小記 iOS 視圖控制器的記憶體申請與釋放普遍規則

作者:不及格的程式員-八神

記憶體管理在iOS程式開發扮演非常重要角色,對這塊處理不好的程式會在實際裝置上發生Crash情況.

對於經常在視圖控制器中用retain聲名的輸出口一定要注意,在dealloc中release它們.
Obj-C聲明的屬性,具有如下特性,將新對象賦值當前屬性,並自動釋放屬性中的舊對象.

1. 在appDelegate.m中如果有一個window輸出口,或者另外加了一個導航視圖控制器或是其它什麼視圖控制器時,在 dealloc 方法中,執行這些輸出口的release方法.而不必在applicationDidFinishLaunching中執行釋放.
2. 在單獨的自訂視圖控制器中,如果在接到記憶體緊缺通知時,會執行didReceiveMemoryWarning方法,它會卸載當前視圖表單,並執行viewDidUnload方法,所以在該方法中將方視圖中的定義的輸出口置為nil. 同時在該視圖的dealloc方法(當該視圖控制項器的release被調用時,該方法被執行)中執行相應的輸出口release方法.
    
   -(void)viewDidUnload
   {
   self.** = nil;
   }

   -(void)dealloc
   {
   [** release];
   [supper dealloc];
   }

3. 執行個體方法,靜態方法,Factory 方法返回的對象的釋方規則,後兩者都不必手動執行release方法,由系統的記憶體池自動維護.
4. 如果我在appDelegate.m檔案中alloc並init一個視圖控制器,然後把它通過導航控制器的initWithRootViewController方法加到其中時,那麼加完之後要釋放那個視圖控制器.Example:　　myController = [[*** alloc] initWithNibName:"***" bundle:nil];
   UINavigationController *navi = [[UINavigationController alloc] initWithRootViewController:myController];
   [myController release];
   [tabController presentModalViewController:navi animated:YES];
   [navi release];
   
5. 在自訂視圖控制器中聲明了變數,但是沒定義相應屬性,這時對象釋放規則同第1條相同.@interface *** : UIViewController
   {
   UIView *_view;
   }
   @end

   @implementation ***
   -(void)loadView
   {
   [supper loadView];
   _view = [[UIView alloc] initWithFrame:[self.view bounds]];
   [self.view addSubview:_view];
   }

   -(void)dealloc
   {
   [_view release];
   [supper dealloc];
   }
   @end

6. 在iPhone3開發基礎教程中的範例切換視圖的代碼問題,我覺得裡面有一個順序寫錯了,之後我在google查了一下,有不少人有同問.@implementation SwitchViewController
   @synthesize blueViewController;
   @synthesize yellowViewController;

   - (void)viewDidLoad
   {
   BlueViewController *blueController = [[BlueViewController alloc] initWithNibName:@"BlueView" bundle:nil];
   self.blueViewController = blueController;
   [self.view insertSubview:blueController.view atIndex:0];
   [blueController release];
   }
   
   - (IBAction)switchViews:(id)sender
   {
   [UIView beginAnimations:@"View Flip" context:nil];
   [UIView setAnimationDuration:1.25];
   [UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];
   
   if (self.yellowViewController.view.superview == nil)//這條語句是最有趣的,OBJ-C允許向nil發送訊息.
   {
   if (self.yellowViewController == nil)
   {
   YellowViewController *yellowController =
   [[YellowViewController alloc] initWithNibName:@"YellowView"
   bundle:nil];
   self.yellowViewController = yellowController;
   [yellowController release];
   }
   [UIView setAnimationTransition:UIViewAnimationTransitionFlipFromRight forView:self.view cache:YES];
   [blueViewController viewWillAppear:YES];
   [yellowViewController viewWillDisappear:YES];
   [blueViewController.view removeFromSuperview];
   [self.view insertSubview:yellowViewController.view atIndex:0];
   [yellowViewController viewDidDisappear:YES];
   [blueViewController viewDidAppear:YES];
   }
   else
   {
   if (self.blueViewController == nil)
   {
   BlueViewController *blueController =
   [[BlueViewController alloc] initWithNibName:@"BlueView"
   bundle:nil];
   self.blueViewController = blueController;
   [blueController release];
   }
   //[UIView setAnimationTransition:
   // UIViewAnimationTransitionFlipFromLeft
   // forView:self.view cache:YES];

   //[yellowViewController viewWillAppear:YES];
   //[blueViewController viewWillDisappear:YES];
   [yellowViewController.view removeFromSuperview];
   [self.view insertSubview:blueViewController.view atIndex:0];
   //[blueViewController viewDidDisappear:YES];
   //[yellowViewController viewDidAppear:YES];
   }
   //[UIView commitAnimations];
   }

   - (void)didReceiveMemoryWarning
   {
   [super didReceiveMemoryWarning];
   if (self.blueViewController.view.superview == nil)
   self.blueViewController = nil;
   else
   self.yellowViewController = nil;
   }

   - (void)dealloc
   {
   [yellowViewController release];
   [blueViewController release];
   [super dealloc];
   }

   @end

7.  
   都在dealloc中執行.我看到在wordPress的iPhone用戶端這樣做的,不過好像它在特意相容iOS3之前的版本,3.0之前的版本並不存在viewDidUnload方法,蘋果的開發手冊上有描述.
    
    
   -(void)dealloc
   {
   [myView release], myView = nil;
   }

   附.
   python /Users/yangiori/Downloads/facebook-three20-309d34e/src/scripts/ttmodule.py -p /Users/yangiori/Documents/iPhoneLiaoBao/iPhoneLiaoBao.xcodeproj Three20 //區分大小寫。。。